[ivanm]

Hi everyone,
I've been using Pentax MX for several years now and quite extensively, I am using it with 50mm f1.4 and 85mm f2.
I have noticed that the images have gradually started becoming less sharp, on both of the lenses, also when the lenses are on more closed f-stops.

I am developing in the same lab as usual, and i there is no decrease in quality of their scans for the photos i take with my mamiya67, so its not the lab. I use fresh films as usual.

I am having doubts about the prism, but even when the focus is spot on (which is getting to be harder than usual) - the sharpness is not what it was, and seems somehow uneven.
Could it be the pressure plate or perhaps the lens mount that is somehow decentered?

Would be very thankful for any feedback!

[Ray-uk]

Hi everyone,
I've been using Pentax MX for several years now and quite extensively, I am using it with 50mm f1.4 and 85mm f2.
I have noticed that the images have gradually started becoming less sharp, on both of the lenses, also when the lenses are on more closed f-stops.

I am developing in the same lab as usual, and i there is no decrease in quality of their scans for the photos i take with my mamiya67, so its not the lab. I use fresh films as usual.

I am having doubts about the prism, but even when the focus is spot on (which is getting to be harder than usual) - the sharpness is not what it was, and seems somehow uneven.
Could it be the pressure plate or perhaps the lens mount that is somehow decentered?

Would be very thankful for any feedback!

I think it is more likely to be the focus screen or mirror that is misaligned. Try removing the screen and refitting it.

[womble]

As Ray said, the screen might be not correctly in the holder. Try unclipping it (so it drops down) and checking.

Alternatively, maybe some foam has gone? I had a Ricoh recently which was hard to focus and it turned-out it was missing a bit of foam from behind the mirror. The pressure plate would only be a problem if it was really loose, and it wouldn't impact the sharpness through the viewfinder.

K.

[Viking42]

Are there any parts of the images in focus? If so, then it's likely a focus problem, as the others have mentioned. But if the whole image is uniformly unsharp, it could be something like the mirror bumper foam starting to disintegrate and the mirror is causing more vibration than it should. Have you looked into the mirror box to check it? If it's crumbly and/or sticky, then it's time to replace it. This is to be expected for a 40+ year old camera. It's a moderately easy DIY job, but any reasonably competent camera repair tech can do this for little money. While you're at it, check the light seals around the door and replace those if they're looking the same.

Another thought - are your lenses clean? Apologies if I'm stating the obvious, and I'm by no means trying to insult your intelligence. But you'd be amazed how many people never clean their lenses, and go around shooting with fingerprints, dust and haze all over the front elements and then blame their camera. Or if they do clean them, how few actually do it properly.

Hope this helps. Good luck finding and fixing this.

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Last edited by Viking42; 04-15-2022 at 04:05 PM.

[ivanm]

Hi all, thank you for the feedback and suggestions!

The lenses are definitely properly cleaned.
The confusing thing is that, even if I am standing parallel to a wall (and at 5.6 or something) some parts of the image, which are at the same distance, are less sharp than the others. I am not talking center vs corners, of course. it just seems uneven, and thats why I thought it has something to do with the pressure plate. Also , I am using these lenses with a digital camera and they are sharp, so I dont think it has anything to do with the lenses.

I have a feeling that the lack of sharpness through the viewfinder is somehow an unrelated issue.

What makes it had to analyse is the fact that its not SO bad, the image are still sharp when seen small, but I like to make prints or crops sometimes, and there I do notice this drop in quality.
I think that the mirror bumper foam is the best theory so far, I will go and get it checked.

Thank you!

[Jonathan Mac]

It seems unlikely that lack of sharpness through the viewfinder and also in the negatives, prints or scans are unrelated. Assuming they have the same source then the pressure plate is out as it doesn't affect the viewfinder. Mirror or prism likewise. It's unlikely to be the same problem in both lenses. The only thing I can think of is that the mount itself is either loose or a hard knock has pushed it back on one side so the lenses are no longer focusing evenly across the whole negative or mirror/screen.

[Viking42]

You can check the mirror bumper foam yourself. Pop the lens off, flip the camera upside down and look inside to the area around the bottom of the prism. Surrounding the prism will be a thin strip of foam. It should look fully intact and, well, like healthy foam should look. If it's crumbly, gooey looking, has bits missing, or there are bits of it sticking to the mirror, then it needs replacement. If it kinda looks OK, then reach in and gently touch it with your finger (avoid touching the prism) - if it's sticky or doesn't return to original shape after being compressed, then it's starting to break down and needs replacement.